During the episode, the icon voices a Spock action figure that Leonard (Johnny Galecki) gifts to his roommate and encourages the highly illogical Sheldon (Jim Parsons) to embrace his "human" form and play with a valuable mint-in-box Star Trek transporter toy.

But what could persuade the anal retentive collector in Sheldon to open the box and destroy the toy's value? In a clip from Thursday's "The Transporter Malfunction" episode exclusive to The Hollywood Reporter, Nimoy's "little Spock" uses logic and reason to help convince Sheldon to live a little using phrases like "illogical" and "fascinating."

Co-creator Chuck Lorretold THR at Big Bang's 100th episode party last year that the episode in which Penny (Kaley Cuoco) gives Sheldon a Nimoy-signed napkin -- complete with his DNA -- stands as his favorite "nerd moment" on the long-running series.

“[Sheldon] was so overcome with affection for her, he physically hugged her, which he can’t do as a character," he said at the time. "We all stood there on the stage and everybody got all fablungent and weepy. It was a moment that rose above the show and became something else.”

Check out the clip, above, to see just who says "Set phasers to dumb." The Big Bang Theory airs Thursdays at 8 p.m. on CBS.